The present invention relates to a sample introduction section of an ICP analyzer for trace elements in a fluid.
FIG. 7 is a drawing showing the structure of an inductive plasma mass spectrometer of the related art. This device can be generally classified into a plasma emission section, an analyzing section, and a detecting section. Sample fluid 8 is turned into fine spray by a nebulizer 4 and introduced into a spray chamber 1. The spray chamber selects more minute spray particles of the sample 8 and guides them into a plasma torch 26. In the plasma torch 26, a high frequency is applied by a work coil 28 to gas supplied using a gas controller 27, to generate plasma. The sample 8 is introduced into this plasma and ionized. The ionized sample 8 is analyzed in the analyzer tube 31, and sent to a detector 32. Received information is converted into a signal in the detector 32, and sent to a data processing section 33 for quantitative and qualitative analysis.
A spray chamber of the related art, can be a Scott type having a double barrel (two tube) structure, as shown in FIG. 5, or a cyclon type, being barrel shaped, as shown in FIG. 6.
A general spray chamber, has a function of sorting only a sample 81 having a spray of small particles from the sample fluid 8 atomized by the nebulizer 4. As shown in FIG. 7, the finely misted sample 81 passes through a sample outlet pipe 21 and is introduced into the plasma torch 26.
The plasma torch 26 has the function of generating an argon plasma 30, and introducing the finely misted sample 81 into the argon plasma. The principle for generating argon plasma is to apply a high frequency from a high frequency power source 29 and work coil 28 using an inductive coupling method to argon gas introduced from a gas controller, and generate plasma by electrical discharge.
The nebulizer 4 has the function of atomizing the sample fluid 8. FIG. 4 is a structural diagram of the nebulizer 4, and it has a double barrel structure overall. A carrier gas 7 gushing from a gap between the inner tube 5 and the outer tube 6 of the double barrel structure sucks up the sample 8 inside the inner tube 5 and atomizes it.
The Scott type spray chamber 2 atomizes a sample 8 from the nebulizer 4 along an axis. Large spray particles collide with the walls of the spray chamber 2 due to their weight and inertia, and are ejected from a drain 9. Thus, only fine particles are introduced into the plasma torch 26.
The cyclon type spray chamber atomizes the sample 8 so that spray particles swirl. Spray of large particles collides with the inner walls and is expelled from the drain 9, so only spray of fine particles passes through the centrally inserted sample outlet pipe 21 and is introduced into the plasma inside the plasma torch 26.
With the spray chamber of the related art, it is necessary to efficiently expel portions of the atomized spray having large particles to the drain 9. The proportion of the sample 8 introduced into the plasma depends on the particle diameter distribution of the atomized particles, but there is a problem that in the case where a normal nebulizer 4 is used, this is as low as around 2%. Also, if the diameter and length of the spray chamber is changed to increase the proportion of the sample introduced, there is a problem in that the plasma becomes unstable, and the measurement accuracy decreases. In the worst case, it becomes impossible to maintain the plasma, and it is impossible to avoid interrupting measurement. Also, in the case of ICP-MS, interference attributable to the solvent increases. The analytical performance of particles subjected to the resultant interference therefore deteriorates slightly.
For example, argon constituting the plasma combines with oxygen in the solvent (usually water) to become argon oxide, and exerts an influence. Also, heavy rare earth elements are subject to the influence of light rare earth elements.
The present invention solves the above described problems, and an object of the present invention is to improve the efficiency of introducing a sample 8 into plasma without making the plasma unstable, suppress the influence on sample elements attributable to a solvent, and improve analysis performance.
With the present invention, in a spray chamber for separating particle diameters of the spray, spray particles of a sample from the nebulizer that have been atomized inside the spray chamber are heated and made smaller by heating of a central portion of the spray chamber. Also, the periphery of the spray chamber is cooled, and even if there is water vapor present a solvent component, inside the spray, this solvent component is condensed. Further, large diameter particles are caused to attach to the inner wall surface of the middle tube by causing the spray to swirl. With the present invention, the spray chamber has, for example, a triple tube structure comprising an inner tube, a middle tube and an outer tube, with the two ends of the inner tube being open, two end surfaces reaching from the inside of the inner tube to the middle tube and the outer tube being hermetically sealed. A heating member is fitted into the inner tube, a cooling layer is provided between the middle tube and the outer tube, and mist nebulized by the nebulizer is introduced between the inner tube and the middle tube, passed through, and ejected.